//
//  Video.hpp
//  Clock Signal
//
//  Created by Thomas Harte on 04/10/2019.
//  Copyright © 2019 Thomas Harte. All rights reserved.
//

#pragma once

#include "Outputs/CRT/CRT.hpp"
#include "ClockReceiver/ClockReceiver.hpp"
#include "ClockReceiver/DeferredQueue.hpp"

#include <vector>

// Testing hook; not for any other user.
class VideoTester;

namespace Atari::ST {

struct LineLength {
	int length = 1024;
	int hsync_start = 1024;
	int hsync_end = 1024;
};

/*!
	Models a combination of the parts of the GLUE, MMU and Shifter that in net
	form the video subsystem of the Atari ST. So not accurate to a real chip, but
	(hopefully) to a subsystem.
*/
class Video {
public:
	Video();

	/*!
		Sets the memory pool that provides video, and its size in words.
	*/
	void set_ram(uint16_t *, size_t size);

	/*!
		Sets the target device for video data.
	*/
	void set_scan_target(Outputs::Display::ScanTarget *scan_target);

	/// Gets the current scan status.
	Outputs::Display::ScanStatus get_scaled_scan_status() const;

	/*!
		Sets the type of output.
	*/
	void set_display_type(Outputs::Display::DisplayType);

	/*!
		Gets the type of output.
	*/
	Outputs::Display::DisplayType get_display_type() const;

	/*!
		Produces the next @c duration period of pixels.
	*/
	void run_for(HalfCycles duration);


	/*!
		@returns the number of cycles until there is next a change in the hsync,
		vsync or display_enable outputs.
	*/
	HalfCycles next_sequence_point();

	/*!
		@returns @c true if the horizontal sync output is currently active; @c false otherwise.

		@discussion On an Atari ST, this generates a VPA-style interrupt, which is often erroneously
		documented as being triggered by horizontal blank.
	*/
	bool hsync();

	/*!
		@returns @c true if the vertical sync output is currently active; @c false otherwise.

		@discussion On an Atari ST, this generates a VPA-style interrupt, which is often erroneously
		documented as being triggered by vertical blank.
	*/
	bool vsync();

	/*!
		@returns @c true if the display enabled output is currently active; @c false otherwise.

		@discussion On an Atari ST this is fed to the MFP. The documentation that I've been able to
		find implies a total 28-cycle delay between the real delay enabled signal changing and its effect
		on the 68000 interrupt input via the MFP. As I have yet to determine how much delay is caused
		by the MFP a full 28-cycle delay is applied by this class. This should be dialled down when the
		MFP's responsibility is clarified.
	*/
	bool display_enabled();

	/// @returns the effect of reading from @c address; only the low 6 bits are decoded.
	uint16_t read(int address);

	/// Writes @c value to @c address, of which only the low 6 bits are decoded.
	void write(int address, uint16_t value);

	/// Used internally to track state.
	enum class FieldFrequency {
		Fifty = 0, Sixty = 1, SeventyTwo = 2
	};

	struct RangeObserver {
		/// Indicates to the observer that the memory access range has changed.
		virtual void video_did_change_access_range(Video *) = 0;
	};

	/// Sets a range observer, which is an actor that will be notified if the memory access range changes.
	void set_range_observer(RangeObserver *);

	struct Range {
		uint32_t low_address, high_address;
	};
	/*!
		@returns the range of addresses that the video might read from.
	*/
	Range get_memory_access_range();

private:
	DeferredQueue<HalfCycles> deferrer_;

	Outputs::CRT::CRT crt_;
	RangeObserver *range_observer_ = nullptr;

	uint16_t raw_palette_[16];
	uint16_t palette_[16];
	int base_address_ = 0;
	int previous_base_address_ = 0;
	int current_address_ = 0;

	uint16_t *ram_ = nullptr;
	int ram_mask_ = 0;

	int x_ = 0, y_ = 0, next_y_ = 0;
	bool load_ = false;
	int load_base_ = 0;

	uint16_t video_mode_ = 0;
	uint16_t sync_mode_ = 0;

	FieldFrequency field_frequency_ = FieldFrequency::Fifty;
	enum class OutputBpp {
		One, Two, Four
	} output_bpp_ = OutputBpp::Four;
	void update_output_mode();

	struct HorizontalState {
		bool enable = false;
		bool blank = false;
		bool sync = false;
	} horizontal_;
	struct VerticalState {
		bool enable = false;
		bool blank = false;

		enum class SyncSchedule {
			/// No sync events this line.
			None,
			/// Sync should begin during this horizontal line.
			Begin,
			/// Sync should end during this horizontal line.
			End,
		} sync_schedule = SyncSchedule::None;
		bool sync = false;
	} vertical_, next_vertical_;
	LineLength line_length_;

	int data_latch_position_ = 0;
	int data_latch_read_position_ = 0;
	uint16_t data_latch_[128];
	void push_latched_data();

	void reset_fifo();

	/*!
		Provides a target for control over the output video stream, which is considered to be
		a permanently shifting shifter, that you need to reload when appropriate, which can be
		overridden by the blank and sync levels.

		This stream will automatically insert a colour burst.
	*/
	class VideoStream {
	public:
		VideoStream(Outputs::CRT::CRT &crt, uint16_t *palette) : crt_(crt), palette_(palette) {}

		enum class OutputMode {
			Sync, Blank, ColourBurst, Pixels,
		};

		/// Sets the current data format for the shifter. Changes in output BPP flush the shifter.
		void set_bpp(OutputBpp bpp);

		/// Outputs signal of type @c mode for @c duration.
		void output(int duration, OutputMode mode);

		/// Warns the video stream that the border colour, included in the palette that it holds a pointer to,
		/// will change momentarily. This should be called after the relevant @c output() updates, and
		/// is used to help elide border-regio output.
		void will_change_border_colour();

		/// Loads 64 bits into the Shifter. The shifter shifts continuously. If you also declare
		/// a pixels region then whatever is being shifted will reach the display, in a form that
		/// depends on the current output BPP.
		void load(uint64_t value);

	private:
		// The target CRT and the palette to use.
		Outputs::CRT::CRT &crt_;
		uint16_t *palette_ = nullptr;

		// Internal stateful processes.
		void generate(int duration, OutputMode mode, bool is_terminal);

		void flush_border();
		void flush_pixels();
		void shift(int duration);
		void output_pixels(int duration);

		// Internal state that is a function of output intent.
		int duration_ = 0;
		OutputMode output_mode_ = OutputMode::Sync;
		OutputBpp bpp_ = OutputBpp::Four;
		union {
			uint64_t output_shifter_;
			uint32_t shifter_halves_[2];
		};

		// Internal state for handling output serialisation.
		uint16_t *pixel_buffer_ = nullptr;
		int pixel_pointer_ = 0;
	} video_stream_;

	/// Contains copies of the various observeable fields, after the relevant propagation delay.
	struct PublicState {
		bool display_enable = false;
		bool hsync = false;
		bool vsync = false;
	} public_state_;

	friend class ::VideoTester;
};

}
